1. Field of the Invention
The present invention relates to a high-density mounted module containing an active component such as a semiconductor etc. and a passive component such as a resistor, a capacitor, etc.
2. Description of the Prior Art
Recently, with a demand for high performance and miniaturization of electronic equipment, high density and high performance of a semiconductor have been increasingly desired. This leads to a demand for a small size and high-density circuit substrate on which such a semiconductor is to be mounted. In order to meet such demands, a connection method using an inner via that can connect between wiring patterns of LSIs or components in the shortest distance has been developed in various fields in order to achieve higher density mounting.
However, there is a limitation in mounting components two-dimensionally with high density even with the above-mentioned methods. Furthermore, since these high-density mounted substrates having an inner-via structure are formed of a resin-based material, the thermal conductivity is low. Therefore, as the mounting density of components becomes higher, it is getting more difficult to release heat that has been generated by the components. In the near future, a clock frequency of a CPU is expected to be about 1 GHz. It is estimated that with the sophistication in the function of the CPU, its electric power consumption accordingly will reach 100 W to 150 W per chip. Furthermore, in accordance with high speed and high density, the effect of noise cannot be ignored. Therefore, there is an expectation for a module in which components are contained three-dimensionally, in addition to a circuit substrate with a high-density and high-performance, as well as an anti-noise property and a thermal radiation property.
In order to meet such demands, JP 2(1990)-121392A proposes a module in which a multilayer ceramic substrate is used as a substrate and a capacitor and a register are formed in an internal portion of the substrate. Such a ceramic multilayer substrate is obtained by processing a material that has a high dielectric property and can be fired simultaneously with a substrate material into a sheet and then firing the sheet sandwiched between the substrates. However, in the case where different kinds of materials are fired simultaneously, due to a lag in sintering timing or difference in the shrinkage at the time of sintering, the multilayer substrate may suffer some warping after being fired or an internal wiring may be peeled off. Therefore, it is necessary to control firing conditions precisely. Furthermore, the components involved in a ceramic substrate are based on simultaneous firing as mentioned above. Therefore, it is possible to include a capacitor, a resistor, or the like, but it is impossible to fire a semiconductor of silicon etc., which lacks in thermal resistant property, simultaneously, and thus the semiconductor cannot be contained.
On the other hand, a circuit substrate in which an active component such as a semiconductor etc. and a passive component such as a capacitor, a resistor etc. are contained at low temperatures is proposed. JP 3 (1991)-69191 A and JP11 (1999)-103147 A describe a method including the steps of: mounting electric components onto a copper wiring formed on a printed wiring board material; further coating the entire surface of the printed wiring board with resin so as to form a buried layer; and then adhering a plurality of layers by an adhesive. Furthermore, JP 9 (1997)-214092 A describes a method including the steps of: burying a material such as a dielectric material etc. in a through hole; forming a surface electrode and allowing a capacitor or a resistor to be included. In addition, there also is a method of adding a function of a capacitor etc. into a printed wiring board itself. JP 5 (1995)-7063 A (U.S. Pat. No. 3,019,541) describes a capacitor built-in substrate in which electrodes are formed on both surfaces of the dielectric substrate obtained by mixing dielectric powder and resin. Furthermore, JP11 (1999)-220262 A describes a method for allowing a semiconductor, a capacitor, or the like to be contained in an inner-via structure.
As mentioned above, a conventional three-dimensionally mounted module having an inner via structure capable of realizing a high-density wiring and containing components is classified into two types: a module using a ceramic substrate that is excellent in the thermal radiation property and the air tightness; and a module that can be cured at a low temperature. The ceramic substrate is excellent in the thermal radiation property and capable of containing a capacitor with high dielectric constant, but it is difficult to fire different kinds of materials simultaneously and it is impossible to include a semiconductor. Also, there is a problem from a viewpoint of cost. On the other hand, a printed wiring board that can be cured at low temperatures has a possibility of including a semiconductor and is advantageous from the viewpoint of cost, but it is difficult to obtain a high dielectric constant in the case of a composite material mixing a dielectric material, etc. and resin. This is apparent from an example of the capacitor formed in the through hole or a printed wiring board mixing dielectric powder. In general, the printed wiring board has a low thermal conductivity and inadequate in heat resistance property. Furthermore, the method of sealing a semiconductor or a capacitor, etc. mounted on the printed wiring board with resin to allow a plurality of layers to be contained has a problem in which individual components can be contained but the thickness of the module itself for the individual components to be buried becomes large, and thus it is difficult to reduce the module volume. Furthermore, due to the thermal stress due to the difference of the coefficient of thermal expansion between the contained components and the printed wiring board, steps for providing a buffer layer having a constant coefficient of thermal expansion between the component and the printed wiring board material, adjusting the coefficient of thermal expansion of the printed circuit materials, or the like, are taken. However, the coefficient of thermal expansion of the semiconductor is generally small, and it is extremely difficult to adjust the coefficient of thermal expansion only with a printed wiring board material in the range of operation temperatures.